MICROEARTHQUAKE INVESTIGATION OF THE MESA GEOTHERMAL ANOMALY, IMPERIAL VALLEY, CALIFORNIA

Geophysics ◽  
1977 ◽  
Vol 42 (1) ◽  
pp. 17-33 ◽  
Author(s):  
Jim Combs ◽  
David Hadley
Keyword(s):  
Vertical Component ◽  
Surface Expression ◽  
High Gain ◽  
Strike Slip ◽  
Imperial Valley ◽  
Natural Period ◽  
Near Surface ◽  
Geothermal Fluids ◽  
First Motion ◽  
Motion Studies

Microearthquakes associated with the Mesa geothermal anomaly were recorded for five weeks during the summer of 1973 using an array of six portable, high‐gain seismographs equipped with vertical‐component 1-sec natural period seismometers. Background seismicity of the area is thus determined prior to development for geothermal power and water. The local seismicity changed considerably over the recording period. Most daily activity was characterized by only one or two potentially locatable events, while two microearthquake swarms of two‐ and three‐day duration included as many as 100 or more distinct local events per day. Hundreds of small events (nanoearthquakes), some clustered in swarms, were recorded by each seismograph; however, most were not detected on four or more seismograms so that hypocentral locations usually could not be determined. Locations were determined for 36 microearthquakes having epicenters situated in the [Formula: see text] areal extent of the geothermal anomaly. Focal depths ranged from near‐surface to about 8 km. More than half of the located events have hypocenters greater than the 4.0 km which is approximately the depth to crystalline basement. Stress associated with the Mesa geothermal anomaly is relieved by a combination of continuous microseismic activity and intermittent microearthquake swarms. Based on the results of the present study, a new right‐lateral strike‐slip fault, the Mesa fault, was defined. First motion studies indicate strike‐slip faulting although there is no surface expression of the fault. The northwest‐southeast trending Mesa fault is an active fault functioning as a conduit for rising geothermal fluids of the Mesa geothermal anomaly. This investigation is another demonstration that geothermal areas are characterized by enhanced microearthquake activity.

Microearthquake seismicity and tectonics of Coastal Northern California

1970 ◽  
Vol 60 (5) ◽  
pp. 1669-1699 ◽  
Author(s):  
Leonardo Seeber ◽  
Muawia Barazangi ◽  
Ali Nowroozi
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
San Andreas Fault ◽  
High Gain ◽  
Strike Slip ◽  
Fault System ◽  
Northern California ◽  
Fault Plane Solutions ◽  
Sharp Bend ◽  
San Andreas

Abstract This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes. Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening. The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino. The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.

Aftershocks of the Benham nuclear explosion

1969 ◽  
Vol 59 (6) ◽  
pp. 2271-2281
Author(s):  
R. M. Hamilton ◽  
J. H. Healy
Keyword(s):  
Fault Plane ◽  
Nuclear Explosion ◽  
Test Site ◽  
Strike Slip ◽  
Nevada Test Site ◽  
Ground Zero ◽  
Fault Plane Solutions ◽  
Fault Movement ◽  
Near Surface ◽  
Earthquake Distribution

abstract The Benham nuclear explosion, a 1.1 megaton test 1.4 km beneath Pahute Mesa at the Nevada Test Site, initiated a sequence of earthquakes lasting several months. The epicenters of these shocks were located within 13 km of ground zero in several linear zones that parallel the regional fault trends. Focal depths range from near surface to 6 km. The earthquakes are not located in the zone of the major ground breakage. The earthquake distribution and fault plane solutions together indicate that both right-lateral strike-slip fault movement and dip-slip fault movement occurred. The explosion apparently caused the release of natural tectonic strain.

Are There Better Disposal Methods?

2000 ◽  
Author(s):  
Hans Tammemagi
Keyword(s):  
Sustainable Development ◽  
Waste Disposal ◽  
Surface Expression ◽  
Abandoned Mines ◽  
Underground Mines ◽  
Open Pit ◽  
Near Surface ◽  
The Sustainable Development ◽  
Future Value ◽  
Deep Underground

Most of the solid waste generated by society ultimately winds up in near-surface landfills. Let us put our thinking caps firmly on, place our prejudices aside, and explore what other methods might be used to dispose of waste. We should seek, in particular, the approaches that best fulfill the three basic principles described in chapter 2. That is, we should strive to find disposal methods that are in accord with sustainable development. Existing and abandoned pits, quarries, and mines are attractive for waste disposal because a hole to contain the wastes has already been excavated. Such abandoned areas, when left unreclaimed, cannot be used for agriculture or other beneficial uses. Thus, they generally do not have significant market value and can often be obtained relatively cheaply. For these reasons, pits and quarries have been extensively used for landfills. Operating and abandoned mines, on which this section focuses, are somewhat similar to pits and quarries, though usually larger. Abandoned mines hold promise as disposal facilities because they are resource areas that have been depleted and thus have little future value. There are two basic types of mine: the open pit mine, which is effectively a large pit or hole in the ground; and the underground mine, where the mined-out openings are deep underground and there is no surface expression except for the shafts used to gain subsurface access. Because underground mines occupy minimal surface land, their use for waste disposal would be in accordance with the sustainable development principles that were advocated in chapter 2. Several European countries, with higher population densities and much smaller land mass than in North America, have long used abandoned underground mines to dispose of their rubbish. The major advantage of placing wastes deep in underground mines is that it is inherently safer than placing the wastes in a surface facility. The amount of groundwater and its flow rate decrease with depth; this fact, combined with the long transport paths back to the biosphere, minimizes the possibility that contaminants will be carried by groundwater to the surface, where they could damage the environment. The waste is contained deeper and more securely.

Robust Empirical Time–Frequency Relations for Seismic Spectral Amplitudes, Part 1: Application to Regional S Waves in Southeastern Iran

2020 ◽  
Author(s):  
Maryam Safarshahi ◽  
Igor B. Morozov
Keyword(s):  
Seismic Waves ◽  
Joint Inversion ◽  
Vertical Component ◽  
Transverse Component ◽  
Model Parameters ◽  
S Wave ◽  
Near Surface ◽  
S Waves ◽  
Time Frequency ◽  
Frequency Independent

ABSTRACT Empirical models of geometrical-, Q-, t-star, and kappa-type attenuation of seismic waves and ground-motion prediction equations (GMPEs) are viewed as cases of a common empirical standard model describing variation of wave amplitudes with time and frequency. Compared with existing parametric and nonparametric approaches, several new features are included in this model: (1) flexible empirical parameterization with possible nonmonotonous time or distance dependencies; (2) joint inversion for time or distance and frequency dependencies, source spectra, site responses, kappas, and Q; (3) additional constraints removing spurious correlations of model parameters and data residuals with source–receiver distances and frequencies; (4) possible kappa terms for sources as well as for receivers; (5) orientation-independent horizontal- and three-component amplitudes; and (6) adaptive filtering to reduce noise effects. The approach is applied to local and regional S-wave amplitudes in southeastern Iran. Comparisons with previous studies show that conventional attenuation models often contain method-specific biases caused by limited parameterizations of frequency-independent amplitude decays and assumptions about the models, such as smoothness of amplitude variations. Without such assumptions, the frequency-independent spreading of S waves is much faster than inferred by conventional modeling. For example, transverse-component amplitudes decrease with travel time t as about t−1.8 at distances closer than 90 km and as t−2.5 beyond 115 km. The rapid amplitude decay at larger distances could be caused by scattering within the near surface. From about 90 to 115 km distances, the amplitude increases by a factor of about 3, which could be due to reflections from the Moho and within the crust. With more accurate geometrical-spreading and kappa models, the Q factor for the study area is frequency independent and exceeds 2000. The frequency-independent and Q-type attenuation for vertical-component and multicomponent amplitudes is somewhat weaker than for the horizontal components. These observations appear to be general and likely apply to other areas.

Mineralogy of the near-surface expression of Au-As-Cu mineralization in an arid environment

1994 ◽  
Vol 58 (391) ◽  
pp. 315-323
Author(s):  
R. Bogoch ◽  
M. Shirav ◽  
A. Gilat ◽  
L. Halicz
Keyword(s):  
Iron Oxide ◽  
Surface Expression ◽  
Arid Environment ◽  
Solid Solution Phase ◽  
Near Surface ◽  
Amorphous Phases ◽  
Fine Grained ◽  
Precambrian Terrain ◽  
Spherical Droplets ◽  
Neutral Conditions

AbstractIn the arid, Late Precambrian terrain of southern Israel, a complex suite of minerals and amorphous species were deposited in host gneiss from fluids under near-neutral conditions within 1 m of the surface. The morphology of secondary gold appears to relate to its host mineral (skeletal-dendritic with quartz; multi-faceted crystals with arsenates; spherical droplets with iron oxide). The gold is very fine-grained, and was most likely complexed as a thiosulphate.Three amorphous phases are present (iron oxide, chrysocolla, Cu-Mn-(Fe-As) silicate). At least in part, gold and baryte appear to have crystallized out of a metal-Fe-oxide gel. Other minerals, including apatite, anglesite, and conichalcite, may have grown from appropriate crystallites present in the gel.The conichalcite occurs mainly as bladed to acicular radial spherulites. In the presence of lead, a solid solution phase between duftite and conichalcite (‘Pb-conichalcite’) was formed.

A reevaluation of the position of the Baie Verte – Brompton Line in the Quebec Appalachians: the influence of Middle Devonian strike-slip faulting in Gaspé Peninsula

1992 ◽  
Vol 29 (6) ◽  
pp. 1265-1273 ◽  
Author(s):  
Michel Malo ◽  
Donna Kirkwood ◽  
Gilles De Broucker ◽  
Pierre St-Julien
Keyword(s):  
Middle Devonian ◽  
Surface Expression ◽  
Strike Slip ◽  
Aeromagnetic Data ◽  
Geological Data ◽  
Appalachian Orogen ◽  
Eastern Townships ◽  
Gaspe Peninsula ◽  
Gaspé Peninsula

The Baie Verte – Brompton Line (BBL), the surface expression of the Taconian suture in the Canadian Appalachian Orogen, extends from southern Quebec to the northeast end of Newfoundland. In the Quebec Appalachians, the BBL was previously located under the post-Taconian cover rocks between the Eastern Townships and Gaspé Peninsula. New geological data and reinterpretation of gravimetric and aeromagnetic data suggest that the BBL follows the southern edge of the Cambrian–Ordovician rocks of northern Gaspé Peninsula and is displaced by Middle Devonian strike-slip faults on the southern part of the peninsula. On a pre-Middle Devonian palinspastic map, the BBL is parallel to the Quebec Reentrant – St. Lawrence Promontory and the Appalachian structural front.

scholarly journals An Improved Second-Moment Closure Model of Langmuir Turbulence

2015 ◽  
Vol 45 (1) ◽  
pp. 84-103 ◽  
Author(s):  
Ramsey R. Harcourt
Keyword(s):  
Surface Defects ◽  
Solid Wall ◽  
Vertical Component ◽  
Force Production ◽  
Reynolds Stress Model ◽  
Moment Closure ◽  
Langmuir Turbulence ◽  
Near Surface ◽  
Second Moment ◽  
Second Moment Closure

AbstractA prior second-moment closure (SMC) model of Langmuir turbulence in the upper ocean is modified by introduction of inhomogeneous pressure–strain rate and pressure–scalar gradient closures that are similar to the high Reynolds number, near-wall treatments for solid wall boundaries. This repairs several near-surface defects in the algebraic Reynolds stress model (ARSM) of the prior SMC by redirecting Craik–Leibovich (CL) vortex force production of turbulent kinetic energy out of the surface-normal vertical component and into a horizontal one, with an associated reduction in near-surface CL production of vertical momentum flux. A surface-proximity function introduces a new closure parameter that is tuned to previous results from large-eddy simulations (LES), and a numerical SMC model based on stability functions from the new ARSM produces improved comparisons with mean profiles of momentum and TKE components from steady-state LES results forced by aligned wind and waves. An examination of higher-order quasi-homogeneous closures and a numerical simulation of Langmuir turbulence away from the boundaries both show the near-surface inhomogeneous closure to be both necessary for consistency and preferable for simplicity.

Interpretation of three-dimensional seismic refraction data from western Hecate Strait, British Columbia: structure of the crust

1993 ◽  
Vol 30 (7) ◽  
pp. 1440-1452 ◽  
Author(s):  
J. A. Hole ◽  
R. M. Clowes ◽  
R. M. Ellis
Keyword(s):  
Velocity Structure ◽  
Seismic Refraction ◽  
Three Dimensional ◽  
Surface Expression ◽  
Wide Angle ◽  
Lateral Velocity ◽  
Near Surface ◽  
Velocity Anomaly ◽  
Air Gun ◽  
Refraction Data

As part of a multidisciplinary investigation of the structure and tectonics of the Queen Charlotte Basin and underlying crust, deep multichannel seismic reflection and coincident crustal refraction data were collected in 1988. Energy from the reflection air-gun array source was recorded at land sites at offsets appropriate to record crustal refraction and wide-angle reflection data. Refraction data recorded in a broadside geometry provide good three-dimensional coverage of western Hecate Strait. These data are modelled using tomographic inversion techniques to determine the three-dimensional velocity structure of the crust in this region. The one-dimensional average velocity increases rapidly with depth to 6.5 km/s at 7 km depth. Velocities from 7 to at least 12 km depth remain approximately constant and are associated with rocks of the Wrangellia terrane. Significant lateral velocity variations, including large differences in near-surface velocities attributable to surface features, relatively low velocities representing interbedded Tertiary sediments and volcanics, and a deep high-velocity anomaly that may represent the root of an igneous intrusion, are mapped. Wide-angle reflections from the Moho are used to determine the thickness of the crust. The Moho is at 29 km depth beneath the east coast of the Queen Charlotte Islands. This is deeper than the Moho observed below Queen Charlotte Sound and as deep as, or deeper than, that below Hecate Strait. Crustal thinning during Tertiary extension was thus greatest beneath the surface expression of the Queen Charlotte Basin, leaving the crust under the islands considerably thicker than under the basin. In an alternate or additional explanation, compression at the continental margin during the last 4 Ma may have been taken up by thickening or underplating of the continental crust beneath the islands. If the Pacific plate is subducting beneath the islands, the Moho observations constrain the slab to dip greater than 20–26°.

scholarly journals Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 Imperial Valley, California, earthquake

1983 ◽  
Vol 73 (6A) ◽  
pp. 1553-1583
Author(s):  
Stephen H. Hartzell ◽  
Thomas H. Heaton
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
The United States ◽  
Strike Slip ◽  
Body Waves ◽  
Rupture Velocity ◽  
Fault Rupture ◽  
Imperial Valley ◽  
History Of ◽  
Strong Ground

Abstract A least-squares point-by-point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 Imperial Valley, California, earthquake. The Imperial fault is represented by a plane embedded in a half-space where the elastic properties vary with depth. The inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right-lateral strike-slip and normal dip-slip components of motion. Inversions are run for different fault dips and for both constant and variable rupture velocity models. Effects of different data sets are also investigated. Inversions are compared which use the strong ground motions alone, the teleseismic body waves alone, and simultaneously the strong ground motion and teleseismic records. The inversions are stabilized by adding both smoothing and positivity constraints. The moment is estimated to be 5.0 × 1025 dyne-cm and the fault dip 90° ± 5°. Dislocation in the hypocentral region south of the United States-Mexican border is relatively small and almost dies out near the border. Dislocation then increases sharply north of the border to a maximum of about 2 m under Interstate 8. Dipslip motion is minor compared to strike-slip motion and is concentrated in the sediments. The best-fitting constant rupture velocity is 80 per cent of the local shear-wave velocity. However, there is a suggestion that the rupture front accelerated from the hypocenter northward. The 1979 Imperial Valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border.

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